Sure no problem:
There you go the php part:
<nav id="menu">
<?php
$args = array(
'menu' => 'mainmenu',
echo' => true,
'fallback_cb' => 'wp_page_menu',
'items_wrap' => '<ul>%3$s</ul>',
'depth' => 0
);
wp_nav_menu( $args );?>
<div class="description">
<?php if(have_posts()):while(have_posts()):the_post();
the_content();
endwhile; endif;?>
</div>
</nav>
Jquery part:
$(".description").appendTo("li.current-menu-item");
dont forget to put it in the document ready statement.